Field of the Invention
The present invention generally relates to an enhanced call server for the optimization of the gateway resources in a telecommunication network based on the IMS (Internet protocol Multimedia Subsystem) architecture.
IMS is based on Internet standards which are currently the major way to deliver services on new networks. It uses the Session Initiation Protocol (SIP) for establishing, managing and terminating sessions. The overall IMS architecture uses a number of components to enable multimedia based sessions between two or more end devices.
A core IMS network is used for interconnecting various types of telecommunication networks. A gateway is placed at the border of a core IMS network for linking it to a peripheral network that may be not based on the IMS architecture. A gateway can receive incoming traffic, i. e. traffic from a peripheral network to the core network, this incoming traffic being in transit or terminating in this gateway. A gateway can also send outgoing traffic i. e. traffic from the core network to a peripheral network, this outgoing traffic being in transit in the core gateway.
This traffic is triggered by different sessions coming from various peripheral networks. These sessions have classically various priority levels. In particular emergency calls have a high priority. Low priority calls may be rejected by a call server if a gateway is congested.
It is difficult, for a network operator, to estimate the outgoing traffic and the terminating traffic to be supported by the gateways of an IMS core network, because these traffics are varying with time.
Description of the Prior Art
Classically, an operator dimensions the resources of each gateway by taking into account the maximal expected traffic outgoing via this gateway, this outgoing traffic being the sum of several traffics originating from all the peripheral networks generating traffic towards this gateway. The resources respectively assigned for the traffics from the peripheral networks are then static. Each peripheral network supplies a part of the load to be supported, and each of them has the same weight and priority when sessions, coming from those networks, are set up. Unfortunately, the traffic load supplied by a given peripheral network varies with time. So each peripheral supplies its maximal traffic load at a time that is respectively different for the different peripheral networks.
In order to be sure to provide the number of sessions requested by customers, and fulfil the relevant service level agreements, the operator could consider the maximal outgoing traffic load of each peripheral network. In each media gateway, it should provide resources sufficient for an outgoing traffic corresponding to the sum of the maximal outgoing traffic loads. However each peripheral network supplies a maximal traffic load at a different busy hour.
Similarly, in each media gateway, it should provide resources sufficient for an incoming traffic corresponding to the sum of the maximal incoming traffic loads. However each peripheral network supplies a maximal incoming traffic load at a different busy hour.
So the real traffic is lower than the available resources at any time. This known method leads to over-dimensioning each gateway: The gateway resources are not optimized, and the investment to support the total traffic is costly for the operator.
A known solution consists in providing resources lower than the sum of the maximal traffic loads, and dropping data packets if ever an incoming media gateway or an outgoing media gateway is overloaded. However this solution is unfair: Consider a peripheral network N1 that supplies its maximal traffic load at the time H1 everyday and a peripheral network N2 that supplies its maximal traffic load at the time H2 every day. At the time H2, for instance, a session belonging to the network N2 may be dropped because a media gateway is overloaded, whereas a session belonging to the network 1 may be accepted in spite of the fact the network N2 should have more priority since it has more many traffic to supply at its busy hour H2.
The document US 201/034195 describes a call server for optimizing the use of the resources in a media gateway of a core network, this call server being configured to:                receive a session setup request message;        and decide to accept or to reject the session setup request as a function of the load of a gateway controlled by this call server.        
It is configured to retrieve a priority indicator that is related to the specific user initiating the request.
Thus, there is a need to provide a better technical solution for optimizing the gateway resources in a telecommunication network.
This can be solved by applying, the call server according to the invention.